Arrangement or system for operating mechanical rectifiers for alternating current



Nov. 6, 1928. H 1,690,553

R. RUDENBERG ARRANGEMENT OR SYSTEM FOR OPERATING MECHANICAL RECTIFIERS FOR ALTERNATING CURRENT Filed Dec. 1, 1925 MMHAM Patented" Nov. 6,

UNITED STATES iAraNtYoFF1ce.

REINHOLD B'fiDENBEBGgOI BEBLDT-GBUNEWALD, GERMANY, ABSIGNOB TO SIEMENS- SCHUGKERTWERKE GESELLSCHAFT MIT BESCHRANKTEB HAFTUNG, OF SIEMENS- STADT, NEAR BERLIN,- GERMANY, A GERMAN CORPORATION.

, ABBANGEMENT OR SYSTEM FOR OPERATING MECHANICAL BECTIIIEBS FOB ALTER- NATING CURRENT.

Application filed December 1, 1925, Serial 1%. 72,608, and in Germany December 12, 1924.

My invention relates to an arrangement or system for operating mechanical rectifiers for alternating current.

In mechanical rectifiers which convert 6 high tension alternating current intov direct current. strong sparking-frequently occurs at the-leading as-well as at the trailing edge of the contact segments. Researches have proven that the sparking at the trailing edge W is due to the fact that immediately after the contact break a considerable pressure difference develops between the two separating edges; 1

In the accompanying drawings I have illustrated my invention by graphs and by a wiring diagram,

Figs. 1 and 2 representing explanatory graphs which show the conditions generally existing during mechanical rectification,

Figs. 3 and 4 representinggraphs illustrating the conditions existing according to the present improvement, and

Fig. 5 representing a diagrammatic illustration of a mechanical rectifier and its cir- 95 cuit connections according to the present invention.

The conditions usually existing during mechanical high voltage rectification as heretofore practiced are illustrated in Fig? ures 1. and 2 of the drawing. The curve nating current, the negative half having been turned upwards owing to the action of the rectifier usuall provided. The rotating- 3'5 arms of the recti er feed the consumer .di rectly during the part E. of this voltage shown in heavy lines. In the meantime the contact with the feeding transformer is interrupted and the consumer has only the 40 natural voltage 6 determined by its-capacity which after the contact is, broken devcreases in amplitude almost according to an exponential curve depending upon the size of the current consumer and the capacity. Generally the dropping of the voltage e at the consumer will take place with a difl'erent speed from the variation of the pressure E at the transformer. The pressure difference developing hereby is indi-' rated in Fig. 1 by the vertical shading of the area between the curves E and e. This pressure diiferencebetween the stationary and the rotating contacts causes the repeated sparking immediately after the separation of the contacts. The pressure difference increases particularly quickly immediately after the breaking of the contact, if the time constant of the natural voltage of the consumer is relatively small i. e. when the pressure 6 drops quickly;

In Fig. 2 another case is illustrated with a greater time constant of the consumer the moment of break being chosen at a time later than the occurrence of the pressure maximum. While in Fig. 1 the pressure 6 at the consumer has dropped quicker than the pressure'E at the transformer, it drops considerably slower here. A great pressure difference develops in this case also between the contacts moving apart so that also in this case sparking occurs.

These drawbacks are eliminated according to my invention'by chosing the time of contact separation at the rectifier so that the drop characteristic of the voltage applied and that of the natural voltage of the consumer substantially coincide about the time ,when the contacts separate. .Such a characteristic is illustrated in Fig. 3 of the drawmg. The voltage curve E and the curve of v v fthenatural voltage e possess at the moment in Flg. '1 is the voltage curve of the alter when the contacts separate the same tangent t. In this case no pressure difference exists between the contacts travelling apart during a. considerable period subsequent to the running off so that no sparking can occur.

If the transformer voltage E develops sinusoidally and the consumer voltage exponentially, the instant of time may be mathematically determined which must be.

chosen on the sinusoidal transformer voltage curve E for the separation of the contacts,

so that at this instant the tangents to the sine curve and to the consumer voltage curve coincide. In the following T represents the time for which the contact remains closed beyond the maximum value of the sine voltage (see Fig. 3). T represents the time constant] determined by the capacity and the ohmic resistance of the consumer, by which in turn the decrease of the consumer voltage c after the contact break is moment of contact separation.

determined (Figs. 1 4). Accordingly the voltage values E and e and their difi'erential quotients, which represent the tangents to the voltage curves, must be e ual at the f a) repre sents the frequency of the alternating volt- .age supplied, t the period of time commencing with the voltage maximum, ,E according to Fig. 3 the amplitude of the alternat ing voltage, and c the ideal value of thev consumer voltage during the same time period, then the transformer voltage may be expressed by:

' 1 E=E cosine wt (1)- and its change by -wE sine ait The consumer voltage .is on the other hand and its change dt For the moment good E cosine m =e e v -wE sine can I From this follows by division cotangent wT =wT (6) so that for each consumer. with given time constant T a definite most favorable runningoff angle 7 is obtained. For the case illustrated in Fig. 3,the time constant T is equal to two thirds of the half wave period T /2. Therefore is so that for tl1e n1ost favorable running-ofi angle we obtain w'r m ctg. 2.09 =25.5 (s

In the design of the rectifier producing a voltage characteristic according to Fig. 3 of the drawing the sparkin at the moment of running oif is suppresse but at the moment of contact closing a great voltage difference prevails between the natural voltage e and the transformer voltage E' (indicated in broken lines) and this gives rise to impact' oscillations. In order to eliminate these impact oscillations the duration of the contact is according to my invention-so adj sted that atthe moment of the closing of the contact the natural voltage is equal of running ofl' the followmg equations of condition therefore hold E cosine (01 a T=E cosine (.071 (9) whei'ein the duration of the period during which no contact exists is denoted by 7 Since thesum of the three periods is equal to a halfvperiod of the alternating voltage, thus v by'insertion of 7' in the exponent of equation (9) and logarithm-ing the equation of condition for the starting contact period 1- Since according to equation (6) T depends only upon the time constant, the running-on period T is also solely a function of the time constant T.

It is advisable to choose the closingand breaking moment according to my invention for the fully loaded consumen If the load of the rectifier dr0ps,,the time constant of I the natural voltage e also changes and this natural voltage e does now not drop as much as before so that impact oscillations may occur again. These im act oscillations now pass to the negative si e and can therefore not produce any considerable excess voltages. The operation of rectifiers with contact segments correctly dimensioned for full load and adjusted according to my invention does therefore not lead to any disturbing secondary phenomena. 7

In Fig. 5y I have illustrated a mechanical rectifier and its associated circuits by which the results hereinbefore discussed are" obtained. In this-figure, 1 represents an alternating current transformer whose primary is connected to the alternating current mains 11 and whose secondary produces high voltage. The secondary of this transformer is connected by way of the mechanical rectifier 15 and-the consumers lines 7 and 8 to a pulsating direct current consumer which may be of any character. It is indicated in Fig. 5 by a rectangle labeled pulsating D. C. consumer. This consumer receives the pulsating direct current produced by the mechanical rectifier 15 according to well known general principles. The shaft of ing are connected to the two lower segments 2' and 3 whereas the consumers line 7 is connected to the corresponding segments '2 and 3 the. middle point of the high tension secondary being connected to ground. The

consumers line 8 is likewise grounded as shown at 13 so that 1n th s manner both halves of the alternating current wave are utilized for rectification in the well known manner. 4 and5 respectively'are the rotating contact arms for the segment pairs 2, 2

and 3, 3 and are mounted on the shaft driven by motor 6 in such manner that they are transposed at an angle of 90 relatively to each other in order to obtain the rectification of both halves of the alternating current wave. These contact arms 4 and 5 are i nsulated from the shaft by the insulating sleeve 14. In parallel to the consumer are arranged a condenser 9 and an adjustable ohmic resistance 10.

The are lengths of the stationary contact pairs 2, 2 and 3, 3' are dimensioned such that in accordance with the graph represented by Fig 4 they will remain in contact with their respective rotating contact arms only during a portion of the half Wave or half cycle of the alternating current voltage furnished by 'the transformer. In other Words only during a portion of this half cycle the transformer secondary is connected with the consumer. During the remainder of the half cycle this connection is. interrupted. Nevertheless, during this remaining period a natural voltage reactfo'n exists at the consumer, determined by the own capacity of the (onsumer and by the capacity of condenser 9. This voltage due to the total capacity is equalized during the contactless period over resistance 10. Thereby this voltage at the consumer decays at a rate indicated by the curve 6 in Fig. 4.

age of the consumer determined-by the total capacity of its'circuit coincides in time value with the voltage of thealternat'ng current half wave. The particular values necessary to obtain th's effect may be ascertained from.

the equation -(11). When the conditions For thepurpose of my invention, the arc lengths of given by this equation are fulfilled, the effect" is simultaneously obtained, that as shown in Fig. 4, the reactance volta e of the consumer also coinc'des in time va ue with the voltage existing at the time in the transformer secondary when the rectifier contacts are closed. Thereby the impact oscillations referred to hereinbefore are avoided.

My invention is thus not confined solely to the design of the rectifier itself for produc'ng the voltage characteristics shown in Figs. 3 and 4, but the equalization of the pres sures at the moment of switching in may be attained by correspondingly controlling the exponential curve through insertion of proper auxiliary reactances 9 and 10 referred to hereinbefore.

Various modifications and changes maybe made Without departing from the spirit and the scope of the invention, and I desire, therefore, that only such limitations shall be placed thereon as are imposed by the prior art.

I claim as my invention 1. In an arrangement for producing and feeding a consumer with pulsating direct current from high tension alternating current, in combination a mechanical rectifier comprising cooperating stationary and rotating contact elements in circuit with the alternating current supplied, the contact surface are lengths of said elements being such that the circuit connection between said elements is interrupted before the end of the half cycle of the supplied alternating current is reached, a pulsating direct current consumer circuit connected with said elements and the consumer, said consumer ClIClllt having capaclty and OhIIllC resistance of suitable values to bring the re-' actance voltage of the consumer circuit due to its capacity in timel agreementwith the voltage of the half cycle of the supplied alternating current existing at the time of contact break between said elements.

2.. In an arrangement for producing and feeding a consumer with pulsating direct current from high tension alternating current, in combination a mechanical rectifier comprising cooperating stationary and rotating contact elements in circuit with the alternating current supplied, the contact surface are lengths of said elements being such that the circuit connection between said elements is made only after the beginning of a half cycle of the supplied alternating current and is interrupted before the end of said half cycle, a pulsating direct current consumer circuit connected with said contact elements and. the consumer, said consumer circuit having capacity and ohmic resistance of suitable value, to bring the reactance voltage of the consumer circuit, due to its own capacity, in timely agreement with the voltage of the half cycle of the supplied alternating current existing at the time of contact break between said elements, and to bring the reactance voltage of the consumer circuit to a value equal to the momentary value of the supplied half cycle voltage whaln the contact between said elements is ma e.

3. In an arrangement for producing andfeeding a consumer with pulsating direct iar ca acit and resistance in said consumer circuit, the capacity of said consumer and said auxiliary capacity being suitably dimensioned to bring the reactance voltage of the consumer circuit due to itslocal capacity in timely agreement withthe voltage of the half cycle of the supplied alternating current existing at the time of contact break between said two elements.

4. In an arrangement for producing and feeding a consumer with pulsating direct current from high tension alternating current, in combination a mechanical rectifier comprising cooperating stationary and rotating contact elements in circuit with the alternating current supplied, the contact surface are lengths of said elements being such that the circuit connection between said elements is made only after the beginning of a half cycle of the supplied alternating current and is interrupted before the end of said half cycle, a pulsating direct current consumer circuit connected with said contact elements and the consumer, said consumer having capacity and ohmic resistance, an auxiliary capacity and resistance in said consumer circuit, the capacity of said consumer and said auxiliary capacity being suitably dimensioned to bring the reactance voltage of the consumer circuit due to its totalcapacity in timely agreement with the voltage of the half cycle of the supplied alternating current existing at the time of contact break between said two elements,

and to bring the reactance voltage of the consumer circuit to a value equal to the momentary value of the supplied half -cycle voltage when the contact between said elements is made.

In testimony whereof I aflix my signature.

REINHOLD RI'TDENBERG. 

